The shame of it. I have become the type of driver I once despised: a 30-something woman with child, driving a large 4x4 needlessly in leafy south-west London. All that's missing is an irritating "Baby on board" sign.

Even if it is gold (or Ipanema Sand, with Arabica leather interior, in brochure-speak). We've been driving it since spring and, like Sean Connery, it's improved with age.

From the stunningly plush leather and wood interior, the excellent front-seat lumbar support, the sat-nav that automatically shows petrol stations when you're down to your last 50 miles of fuel, the 360-degree parking cameras and the DVD screens smartly sunk in the headrests, to the commanding driving position, touch-screen infotainment design, Harman Kardon Logic seven-speaker sound and clever digital speedo that only highlights the numbers the dial is hovering between, it's a fabulous piece of kit.

And that's before you've tested its staggering off-road capacity, which my colleague Andrew English did recently, and which should be mandatory for all new owners in order that they appreciate the fabulous British engineering involved, regardless of whether they ever plan to off-road in it again.

Admittedly there are downsides to driving such a monolith, notably, and predictably, fuel consumption. We chose the V8 petrol version to see if it could ever be justified in this age of financial and environmental austerity.

I wasn't expecting 30mpg, but I was hoping for more than the 15.2mpg that, until last week, was the highest I'd managed to achieve in conditions of mostly 60mph A-roads. The official EU Combined figure is 19mpg - a figure I never saw, let alone the 27.2mpg it should achieve in Extra Urban conditions.

Six days ago, however, the onboard computer suddenly showed a giddy 17.2mpg average fuel consumption. It must have sensed I was about to give it its end-of-term report (or, more likely, the engine has started to bed in), because I haven't altered my driving style, which has been super-economical - I don't touch the brakes unless I'm in imminent danger of a collision, I don't step on the throttle (except for a couple of overtaking manoeuvres when the acceleration of this beast, which weighs the same as a small bungalow, is staggering), I look as far ahead as possible and try to anticipate any change of speed... all good driving practice anyway, but important when you're spending £100 on petrol for every 300 miles travelled.

On the upside, such horrific gas-guzzling means that my 12-week-old baby is a wonderful sleeper, because I can't afford to drive him round at night to soothe him, so he's had to take his chances in the Moses basket.

But is there seriously any point to this £82,270 beast (plus an extra £2,400 for the rear DVD screens, £1,060 for the vision assist pack and £1,050 for four-zone air-conditioning)? Not really. But there's no point to donuts either, or Michael McIntyre, or splashing about in puddles... you get my point.

Call it a guilty pleasure if you will, but there are few finer ways of travelling than in a lounge on wheels that accelerates from 0-60 insanely quickly, drives at motorway speeds in near silence and will get you out of trouble that includes sticky fields and equally sticky overtaking situations.

Yes, the diesel version will kill the planet slightly more slowly, but if it's sheer opulence you're after, it's the Autobiography V8 for you.